The ordering information for this contact in the data sheet on page 2 is just SYM-001T-P0.6
So what does the (N) suffix stand for?
In general, the (N) suffix is an internal designator to JST and it calls out for a some modifications to the part, changes in the raw material supplier at the factory, or packaging.
In this case, the suffix (N) designates the quantity change in the reel
There is no official document about it but it can be found in JST FAQ blog:
http://www.jst.com/home14.html --> SM series